Rock drill feeding devices



Dec. 8, 1964 F. G. LEANDER ETAL 3,160,074

ROCK DRILL FEEDING DEVICES 3 SheetsSheet 1 Filed April 11, 1961 i i 1 IL B v 1 mL mv mm Q Dec. 8, 1964 F. G. LEANDER ETAL 3,160,074

ROCK DRILL FEEDING DEVICES 3 Sheets-Sheet 2 Filed April 11, 1961 &\ ll/49 4 2 V ll Wm OW 3 Sheets-Sheet 3 F. G. LEANDER ETAL ROCK DRILL FEEDING DEVICES Dec. 8, 1964 Filed April 11. 1961 mw mm mm Hi m b .OW Wk NV 0M 0 MN mm mm OR 0.0

mm mm mm \m Rm United States Patent RQCK DRILL FEEDING DEVICES Frans Gunnar Leander, Skelleftea, and Gunnar Herman Rosenblad, Stainn, Sweden, assignors to Atlas ilopco Ahtieboiag, Nacha, .slweden, a corporation of Sweden Filed Apr. 11, 1961, Ser. No. 126,359

Claims priority, application weden Apr. 12, 1969 17 Ciaims. (ill. 91-217) This invention relates to rock drill feeding devices incorporating an elongated support along which a rock drill is advanced and retracted by step by step movement performed by means of pneumatically or hydraulically actuated cylinder and piston means.

It is a general object of the invention to provide improved means for feeding a rock drill by this method along a support, characterized particularly by a simple and compact construction which is effective and durable in operation.

A more specific object of the invention is to provide a rock drill feeding device having improved unidirectional locking devices for performing said step by step feeding movement of the rock drill along said support.

Another object of the invention is to provide easy and simplified reversibility of said uni-directional locking means for performing retraction of the rock drill along said support by step by step movement.

Another object of the invention is to use guideways on said support as a means for guiding the rock drill as Well as the feeding device proper by means of its unidirectional locking means, thereby simplifying said support.

Another object of the invention is to provide unidirectional locking means performing a frictional grip on said support.

Another object of the invention is to provide a rock drill feeding device having improved valve means and valve actuation means for performing automatic reciprocation of the cylinder and piston means for operating said uni-directional locking means.

The foregoing and further objects and advantages of the present invention will become apparent hereinafter as this description proceeds, reference being made to the accompanying drawings in which an embodiment of the invention is illustrated by way of example and by which the invention is not limited as it may be carried out in many diiferent ways within the scope of the claims; In the drawings, wherein like parts are designated by like reference characters throughout the several views,-

FIG. 1 is a side view of a rock drill and a feeding device "ice rock drill is attached a feeding device according to the invention. The feeding device comprises two portions being movable in relation to each other by the action of a pressure fluid, one of said portions comprising a cylinder housing 12 and the other a piston rod 13 connected to a piston which is movable in a cylinder bore inside of said cylinder housing 12 for performing preferably a relatively long stroke. One of the movable portions, preferably the cylinder housing, may be connected to the rock drill 10.

The rock drill 19 is pivotally connected to a saddle 14 by means of a bolt 15, FIG. 5. The saddle has opposed longitudinal grooves 16 by which it is slidably carried on the flanges of angle irons 18 of an elongated support 19. The angle irons are attached to a base plate 20 as by welding and are provided at their forward end with a oentralizer 21 of conventional construction for the drill steel 11. A hose from a pressure fluid supply may be connected to the rock drill Ill at the hose connection 22 adjacent the main control valve 23.

The piston rod 13 and the cylinder housing 12 are provided at their rear with uni-directional locking devices, generally designated 24 and 24 respectively, which coact with the elongated support 19 and form reversible uni-directional gripping means, permitting free sliding motion between the locking devices and the angle irons in one direction of the support while gripping the support and preventing movement of the locking devices in the opposite direction. To this end the piston rod 13 has bolted to the end thereof a collared sleeve 25 having axially locked thereto a member 26 by means of a horizontal pivot 27 with protruding opposed ends. Swingably arranged on the ends of the pivot 27 is a locking plate 28 having opposed grooves 29 for sliding engagement with the horizontal flanges of the angle irons 18 of the support 19 in the upright position of the locking plate 28. As soon as the plate 28 is given an inclination from the upright position swinging around the pivot 27, there is performed a gripping action between the edges of the grooves 29 and the flanges of the angle irons 18 of the support 13 whereby the locking plate 28 takes a firm grip of the support 1d. Pivotally arranged on the collared sleeve 25 between its collar and themember 26 is a I reversing sleeve 30, having a radially and rearwardly protruding abutment 31 carrying a transverse handle 32. When contacting the abutment 31 the locking plate 28 is in upright position and unrestricted to swing away I from the abutment 31. The abutment 31 has a rearwardaccording to the invention arranged on an elongated support;

FIG. 2 is a top view of the arrangement in FIG. 1;

FIG. 3 is an enlarged vertical longitudinal sectional view of the feeding device in FIG. 1 during its working stroke and showing in section one of the conduits extending in parallel with the feeding cylinder;

FIG. 4 is an enlarged sectional view on line 4-4 in FIG. 1;

FIG. 5 is an enlarged sectional view on line 5-5 in FIG. 1;

FIG. 6 is an enlarged vertical longitudinal sectional view of the feeding device in FIG. 1 during its return stroke and showing in section the other of the conduits extending in parallel with the feeding cylinder;

FIG. 7 is an enlarged sectional view on line 77 in FIG. 1; and

FIG. 8 is an enlarged sectional view on line 8-8 in FIG. 1. I

In FIG. 1 there is shown diagrammatically a pneumatic rock drill 10 having a drill steel 11, to the rear of which ly protruding stepped portion 33 resting against a flat portion 34 on the member 26 (FIG. 7), said member having an opposed flat portion 35 for cooperation with the. stepped portion 33 of the abutment 31 after turning the reversing sleeve through by the handle 32, as indicated by dotted lines in FIG. 7. Such turning brings the abutment 31 in an opposite position to the position shown in FIG. 3, and as readily seen, reverses the direction in which the locking plate 28 exerts a gripping or locking action on the support by reversing the direction of the swing away from the abutment 31.

In order to bias the locking plate 28 into locking inclination there is provided a spring pressed ball 36 on a? ing to expel the piston rod 13 from the cylinder acts on the piston therein, the locking device 24 will turn around the pivot 27 and will by its grooves 29 grasp the angle irons 18 of the support 19 producing a hold for the feeding force on the rock drill whereby the rock drill is advanced forwardly, e.g. to the left in FIG. 1. Mean while the other locking device 24 by the friction between the grooves 29 and the support will be brought into upright position against the abutment 31 the locking plate 28 now sliding freely on the support so that the rock drill during the working stroke of the feeding device is able to advance freely to the left in FIG. 1. At the end of the working stroke the pressure fluid inlet is connected to the other side of the cylinder chamber on the other side of the piston. As a result the piston together with the piston rod 13 is quickly retracted to the left into the cylinder housing 12, such retraction releasing the hold of the locking device 24 from the angle irons 18 on the support 19 by pivoting the locking plate 28 against the abutment 31 and displacing the locking device 24 together with the piston rod 13 forwardly along the support. Although in some cases the mass of the rock drill 10 and the cylinder housing 12 may be sufiicient to prevent these parts from being thrown rearwardly, ie to the right in FIG. 1, when the locking device 24 is thrown forwardly during the forward movement of the piston rod 13, there is for greater efliciency provided the additional locking device 24 which during such rearward bias of the rock drill and the cylinder housing is pivoted and locks against the support 19. As soon as the piston has reached its end position during the return stroke, i.e. has reached the beginning position for the next working stroke, valve means to be described hereinafter are actuated so that the piston again is'acted upon by pressure fluid from the other side, again expels the piston rod 13, and the locking device 24 again grasps the angle irons 18 of the support 19. Evidently the locking device 24 may with equal results be arranged on the rock drill proper.

By turning the handles 32, 32 and the reversing sleeves 3t}, 36 through 180 the abutments 31, 31 are brought in a position opposed to the position shown in FIG. 1. In such position the locking plates 28, 28 are released for 'pivotal movement in the direction past the former'upstepwise along the support 19 with each stroke of the feeding device 12.

In FIGS 3, ,6 and 8 the arrangement of the cylinder housing 12 according to the invention is shown more in detail. In the embodiment shown the cylinder housing 12 consists of a front portion 38 and a rear portion 39,'and,

and formspart of a pressure fiuid passage 44 between the main control valve 23 of the rock drill ltl'and a control and reduction valve 45 for the feeding device of per se known construction on the front portion 38. a

' rom the control valve 45 there leads a conduit 45 to valve means in the rear portion'39 of the cylinder housing 12,:said valve means comprising in principle two reversing valvetportions. The valve portions are both provided on a single valve body 47 arranged in the form 'of a cylindrical slide valve around the pistonrod 13 The valve body 47 fits tightly and slidingly in a bore 48 being coaxial with the piston rod '13. The slidevalve 47 is provided with two axially separated grooves 49 and 5% and the bore 48 with five grooves 51 55,,of which the groove 53 is connected to the pressure fluid supply over the passages and conduits 44, 46. The grooves 51 and 55 in FIG. 3 are connected to an exhaust 56 for the pressure fluid, the groove 52 is connected by means of a passage 57 to the cylinder chamber portion 58 adjacent the part of the piston which during the return stroke is to be infiuenced by the pressure fluid, and the groove 54 is connected by means of a conduit 59, FIG. 6, to the portion 69 of the cylinder chamber disposed on the other side of the piston. The valve body 47 is furthermore provided with two grooves 61 and 62 or other suitably arranged recesses which coact with a locking means arranged in the rear portion 39 comprising a spring actuated ball member 63 which in coaction with the groove 61 or the groove 62, respectively, is able to keep the valve body 47 in two distinct positions and of which one position is illustrated in FIG. 3 and the other in FIG. 6.

The movement of the valve body 47 inside of the bore 3 48 is additionally limited by abutments formed at the opposed ends of the bore 48 by an annular member 64 and the collared sleeve 37, respectively. Bolts 65, FIGS. 2 and 8, extending between the front, portion 38 and the collared portion 37 keep the different parts 38, 39, 40, 46, 59 and 64 of the cylinder housing tightly assembled. Tightly inserted with a sliding fit in the collared sleeve 37 is a sleeve 66, which likewise has a tight sliding fit against the piston rod 13 movably extending therethrough. The sleeve 66 provides a closure for the cylinder chamber portion 58 and protrudes outwardly to the rear of the collared sleeve 37.

The passage 57 and consequently the portion 58 of the cylinder chamber in the position of the slide valve of FIG. 3 is in communication with the exhaust 56 by means of the groove 52, the groove 49 and the groove 51, while the portion of the cylinder chamber is connected to the pressure fluid supply conduits 44, 46 by means of the passage 59 and the grooves 54, 5t) and 53; In the position of the valve body 47 shown in FIG. 6 the portion 53 of the cylinder chamber is connected to the pressure fluid supply conduits 44-, 46 by means of the passage 57 and the grooves 52, 49 and 53, while the portion 60 of the cylinder chamber is connected to the exhaust 56 by means of the passage 59 and the grooves 54, 50 and 55. 'Ihe piston rod 13 which is displaceable freely and with some radial play axially inside of the valve body 47 is provided with two abutments 67 and 68, respectively, at opposed sides of the valve body 47, one of them, 67, consisting. of a radial surface on the collared sleeve 25 of the locking device 24 arranged on the piston rod 13, and the other, 68, consisting of a radial surface on the piston 69'driving the piston rod 13. The piston 69 is provided with'sealing collars 7t andis fixed to the piston rod by means of a nut 71.

In order to attain a somewhat damped actuation of the valve body 47 and in order to retard thepiston by means of the pressure fluid without the valve body being hit by hard blows especially during the rapid return of the piston, the abutments 67, 63 act upon the. valve body 47. near the end positions of the piston during its reciprocation in the cylinder 40 through the intermediary of springs 72, 73. One of the said springs, 72, is interposed between one 'end of the Valve body 47 and the tightening sleeve 66 to be acted upon by the abutment 6 7, while the other spring, 73, is interposed between the forward end of the valve body'47 and an annular abutment on the member 64,

i into which the abutment 68 of the piston 69 penetrates.

A rubber buffer 74 may be arranged in the head of the connecting member 41 for damping occasional extra hard forward blows of the piston rod 13.

In operation, let it be assumed that the different parts are in the relative positions occupied when the valve body 4'7 has been displaced; to the left into theposition shown in FIG. 3 as a result of a preceding forward movement of the piston 69 together with the piston rod 13, i.e., a movement to the left in the figure, and by means of the abutment 67 by the intermediary of the'sleeve 66 and the spring 72. In this position of the valve body 47 the pressure fluid supply conduits 44, 46 are in communication with the portion 60 of the cylinder chamber while the exhaust 56 communicates with the portion 58 of the cylinder chamber. Influenced by the pressure fluid then firstly the piston rod 13 is pushed rearwardly urging the plate 28 of the locking device 24, which plate during the preceding movement of the piston rod 13 was in upright position, into inclined position to catch and grip the angle irons 18 of the support 19 by means of the grooves 29 in the locking plate 28. Through the action of the pressure fluid the cylinder housing 12 thereupon is pushed forwardly to the left in FIGS. 1-3 and thus feeds the drill forwardly. During this feeding stroke the valve body 47 remains stationary until the abutment 68 at the end of the feeding stroke through the intermediary of the spring 73 acts with such force on the valve body 47 that the ball stop device 63 is overthrown, whereupon the valve body accelerated by the spring 73 rapidly throws over to the right in FIG. 3 into the position in which the valve body is looked through the interaction between the groove 61 and the ball stop 63, i.e. into the position of the slide valve shown in FIG. 6. This puts the portion 69 of the cylinder chamber into communication with the exhaust 56 by means of the conduit 59 and the grooves 54, 50 and 55, and simultaneously therewith the portion 58 of the cylinder chamber is brought into communication with the pressure fluid supply conduits and passages 46, 44 by means of the passage 57 and the grooves 52, 49 and 53. During the following rapid movement of the piston to the left in FIG. 6 the locking plate 28 of the locking device 24 occupies the upright position shown in FIG. 6 and may together with the piston be freely advanced forwardly along the support 19. In FIG. 6 the piston 69 is shown in a position near the end of this movement just before the valve body 47 through the intermediary of the spring 72 and the sleeve 66 will be actuated upon by the abutment 67 for being reversed into position for a new feeding stroke. The locking device 24 looks the rock drill 10 and the cylinder housing 12 against movement to the rear (to the night in FIG. 6) during the return stroke of the piston 69. During continued operation of the feeding device the rock drill is fed forwardly along the support by a step-bystep movement in the described way until the drilling operation is completed. T hereupon, for retraction of the rock drill, the reversing sleeves 3t), 30 are turned through 180 by meaning of the handles 32, 32 for bringing the abutments 31, 31 over to the opposite side of the pivots 27, 27 thereby reversing the gripping direction of the locking plates 28, 28 Continued operation of the feeding device will now retract the rock drill 19 by a step-bystep movement.

Obviously the valve means shown in the figure for reversing the pressure fluid supply from one side of the piston to the other at the reversal points may be formed in other ways. In order to attain the intended function, however, the valve means should be formed in such a way as to snap from one position to the other at the end positions of the piston. If this would not be the case, i.e. if the valve means 47 in the embodiment shown would lack the snap action provided by the stop device 6163, there would appear an equalization of the pressures on the opposed side of the piston especially during its slow movement in the feeding direction, which would result in the piston stopping in the cylinder.

Furthermore it is obvious that the locking device or devices by means of which the feeding device climbs on the support may be modified in several ways and may be replaced by per se wellknown locking devices for rectifying movement, for example wedge cheeks having oblique springs, balls coaching with angular planes etc.

What we claim is:

1. In a rock drill feeding device for progressively feeding and retracting a rock drill slidably supported on an elongated support along which said rock drill is fed and retracted, the combination which comprises a fluid pressure cylinder having a piston reciprocally movable therein under the action of fluid pressure, means for connecting said cylinder to said rock drill for movement thereof along said support upon movement of said cylinder, a piston rod engaging said piston and extending through an end of said cylinder for axial movement with respect thereto upon movement of said piston therein, means for alternately supplying and exhausting pressure fluid at alternate sides of said piston in said cylinder effecting said reciprocal movement, locking means interconnecting the end of said piston rod outside said cylinder with said support and including a tiltable locking plate pivotally mounted at said end of said piston rod and slidably engaging said support, means on said tiltable locking plate and said support forming a frictional locking engagement therebetween when said locking plate is tilted, and control means at said end of said piston rod for selectively permitting and preventing tilting of said locking plate in either axial direction, said frictional lockng engagement effecting a stationary abutment against which said fluid pressure moves said cylinder and said rock drill along said support.

2. In a rock drill feeding device for progressively feeding and retracting a rock drill slidably supported on an elongated support along which said rock drill is fed and retracted, the combination which comprises a fluid pres sure cylinder having a piston reciprocally movable therein under the action of fluid pressure, means for connecting said cylinder to said rock drill for movement thereof along said-support upon movement of said cylinder, a piston rod engaging said piston and extending through an end of said cylinder for axial movement with respect thereto upon movement of said piston therein, means for alternately supplying and exhausting pressure fluid at alternate sides of said piston in said cylinder effecting said support for free slidable movement ther'ealong only when said locking plate is generally perpendicular to said support and for eifecting frictional locking therebetween when said locking plate is tilted out of said perpendicular dispositiom'and control means for predetermining the axial direction in which said locking plate is tilted out of a the perpendicular for effecting unidirectional frictional locking engagement with said piston.

3. In a rock drill feeding device for progressively feedin and retracting a rock drill slidably supported on an elongated support along which said rock drill is fed and retracted, the combination which comprises a fluid pressure cylinder having a piston reciprocally movable therein under the action of fluid pressure, means for connecting said cylindertto said rock drill for movement thereof along said support upon movement of said cylin der, a piston rod engaging said piston and extending through, an end of said cylinder for axial movement with respect thereto upon movement of said piston therein, means for alternately supplying and exhausting pressure fiuid at alternate sides of said pistonin said cylinder effecting said reciprocal movement, unidirectional frictional locking means at the end of said piston rod outside said cylinder for releasably and frictionally engaging said support forming when engaged with said support a stationary abutment against which said fluid pressure acting on one side of said piston moves said cylinder and said rock drill along said support 1 4. A feeding device as recited in claim 3 which also includes additional unidirectional frictional locking means perpendicular disposition; r

on said cylinder for releasably and frictionally engaging said support.

5. A feeding device as recited in claim 3 in which said unidirectional frictional locking means includes a locking plate pivotally mounted at said end of said piston rod and disposed generally perpendicular to said support, means on said locking plate slidably engaging said support for fr e sliding movement with respect thereto only when said locking plate is substantially perpendicular to said support by effecting frictional locking engagement between said plate and said support when said plate is tilted out of said perpendicular disposition, and control means for selecting the axial direction which said locking plate may be tilted out of said substantially perpendicular disposition.

6. A feeding device as recited in claim 4 in which said additional unidirectional friction locking means. includes a locking plate pivotally mounted at an end of said-cylinder and disposed generally perpendicular to said support, means on said locking plate slidably engaging said support for free sliding movement with respect thereto only when said locking plate is substantially perpendicular to said support by effecting frictional locking engagement between said plate and said support when said plate is tilted out of said perpendicular disposition, and control means for selecting the axial direction which said locking plate may be tilted out of said substantially perpendicular disposition. I

7. A feeding device as recited in claim 5 in which said 7 ing and retracting a rock drill slidably supported on an elongated support along which said rock drill is fed and retracted, the combination which comprises a fluid pressure cylinder having a piston reciprocally moveable there in under the action of fluid pressure, means for connecting said cylinder to said rock drill for movement thereof along said support upon movement of said cylinder, a pis-. ton rod engaging said piston and extending through an end of said cylinder for axial movement with respect thereto upon movement of said piston therein, means for alternately supplying and exhausting pressure fluid at alternate sides of said piston in said cylinder effecting said reciprocal movement, tiltable locking plates pivotally mounted respectively on saidcylinder and the end of said piston rod outside'of said cylinder, said locking plates being generally perpendicularly disposed with respect to said support and including means engaging said support for free sliding movement therealong when said locking plates are perpendicular thereto but'eifecting frictional locking engagement with said support when said locking plates are tilted out of'said perpendicular disposition, and

means associated with each said locking plate for controlling the axial direction in which said plates may be tilted out of said perpendicular disposition.

10. A feeding device as recited in claim 9 in which port and slots'in said locking platesengaging said flanges for said free sliding movement therealong, the width of saidslots being correlated with the thickness of said flanges effecting said frictional locking engagement therebetween when said locking plates arertilted outof said ll. A feeding device 'as'recited in claim 9 in which said means for selecting the axial direction in which tilting I of said locking plates is effected includes resilient biasing means effective upon a portion of said locking plate spaced a from the axis of said pivotal mounting therefor, and means for shifting said biasing means from one side of said axis of said pivotal mounting to the other.

12. In a rock drill feeding device for progressivly feed ing and retracting a rock drill slidably supported on an elongated support along which said rock drill is fed and retracted, the combination which comprises a fluid pres sure cylinder having a piston reciprocally movable therein under the action of said fluid pressure, means for connecting said cylinder to rock drill for movement thereof along said support uopn movement of said cylinder, a piston rod engaging said piston and extending through an end of said cylinder for axial movement with respect thereto upon movement of said piston therein, unidirectional frictional locking means at the end of said piston rod outside said cylinder for releasably and frictionally engaging said support forming when engaged with said support a stationary abutment against which said fluid pressure acting on'one side of said piston moves said cylinder and said rock drill along said support, means for supplying and exhausting pressure fluid separately to each opposite side of said piston in said cylinder effecting said reciprocal movement thereof, valve means for controlling said separate supplying and exhausting of pressure fluid alternately to alternate sides of said piston, and means for automatic operation of said valve means at each extreme of travel of said piston in said cylinder.

13. A feeding device as recited in claim 12 inrwhich said valve means comprise an axially shiftable sleeve around said piston rod, and in which said means for automatic operation of said valve include spaced abutments on said piston rod for engaging and axially shifting said sleeve at each extreme end of the travel of said piston.

14. A feeding device as recited in claim 13 which also includes resilient means interposed between said valve and said abutments for cushioning said shifting of said valve by said abutments and resilient means for releasably holding said valve in each of two axial positions into which it is shifted for effecting rapid and positive shifting of said valve from one said position to the other.

15. In a rock drill feeding device for progressively feeding a rock drill slidably supported on an elongated support along which said rock drill is fed and retracted, the combination which comprises'fluid pressure cylinderand-piston device including a fluid pressure cylinder element having a piston element reciprocally movable therein under the action of fluid pressure, means for connecting one of said cylinder-and-piston elements to said rock drill for movement thereof along said support upon movement-of said one element with respect to the other cylinder-and-piston element, a rod portion on said other cylinder-and-piston element extending axially of said rock drill and against which said rock drill is moved along said support upon reciprocating movement of said piston element within said cylinder element in at least one direction axially of said rock drill and said support under the action of said fluid pressure, means for controllably introducing fluid pressure into said cylinder element for actuation of said piston element therein, and uni-directional frictional locking means engaging said rod portion for forming when engaged with said support a stationary abutment against which said cylinder-and-piston device and said rod portion thereof move said rock drill along said support upon relative axial reciprocating movements of said cylinder element and said piston element.

16. A feeding device as recited in claim 15 in which said uni-directional frictional locking means include a locking plate generally disposed perpendicularly to said support and to said rod portion of said reciprocable elements and engaged therewith, and means, on said locking plate slidably engaging said support for free sliding movement with respect thereto only when said locking plate is Posed at a predetermined angle with respect thereto but effecting locking engagement with said support when tilted out of said predetermined angle.

17. A feeding device as recited in claim 16 which also includes a second tiltable locking plate engaging said reciprocable elements and said support for complementary action and movement with respect to said first locking plate whereby feeding of said rock drill along said support selectively in either feeding or retraction directions is achieved upon reciprocation of said reciprocable elements depending upon which of said locking plates is inclined into said support-engaging position upon reciprocation of said reciprocable elements.

References Cited in the file of this patent UNITED STATES PATENTS Hirschberg Dec. 21, 1937 Armington Jan. 2, 1945 Williams et al Mar. 4, 1952 FOREIGN PATENTS Germany Feb. 5, 1959 

1. IN A ROCK DRILL FEEDING DEVICE FOR PROGRESSIVELY FEEDING AND RETRACTING A ROCK DRILL SLIDABLY SUPPORTED ON AN ELONGATED SUPPORT ALONG WHICH SAID ROCK DRILL IS FED AND RETRACTED, THE COMBINATION WHICH COMPRISES A FLUID PRESSURE CYLINDER HAVING A PISTON RECIPROCALLY MOVABLE THEREIN UNDER THE ACTION OF FLUID PRESSURE, MEANS FOR CONNECTING SAID CYLINDER TO SAID ROCK DRILL FOR MOVEMENT THEREOF ALONG SAID SUPPORT UPON MOVEMENT OF SAID CYLINDER, A PISTON ROD ENGAGING SAID PISTON AND EXTENDING THROUGH AN END OF SAID CYLINDER FOR AXIAL MOVEMENT WITH RESPECT THERETO UPON MOVEMENT OF SAID PISTON THEREIN, MEANS FOR ALTERNATELY SUPPLYING AND EXHAUSTING PRESSURE FLUID AT ALTERNATE SIDES OF SAID PISTON IN SAID CYLINDER EFFECTING SAID RECIPROCAL MOVEMENT, LOCKING MEANS INTERCONNECTING THE END OF SAID PISTON ROD OUTSIDE SAID CYLINDER WITH SAID SUPPORT AND INCLUDING A TILTABLE LOCKING PLATE PIVOTALLY MOUNTED AT SAID END OF SAID PISTON ROD AND SLIDABLY ENGAGING SAID SUPPORT, MEANS ON SAID TILTABLE LOCKING PLATE AND SAID SUPPORT FORMING A FRICTIONAL LOCKING ENGAGEMENT THEREBETWEEN WHEN SAID LOCKING PLATE IS TILTED, AND CONTROL MEANS AT SAID END OF SAID PISTON ROD FOR SELECTIVELY PERMITTING AND PREVENTING TILTING OF SAID LOCKING PLATE IN EITHER AXIAL DIRECTION, SAID FRICTIONAL LOCKING ENGAGEMENT EFFECTING A STATIONARY ABUTMENT AGAINST WHICH SAID FLUID PRESSURE MOVES SAID CYLINDER AND SAID ROCK DRILL ALONG SAID SUPPORT. 